Contact rectifier



Patented Mar.'v28, 1939 UNITED STATES o coNTAc'r'nEcTrFiER Richard C. Hitchcock, Bloomfield, N. J., assignor to Westinghouse Electric & Manufacturing I Company, East Pittsburgh. Pa., a corporation of Pennsylvania.

Application June 1, 1935, SerialNo. 24,52 '1 claims. (c1. 17a-366) My invention'relates to rectiers and especially to the rectiflers of the contact type.

An object of my invention is to provide a rec-4 Other objects of my invention will become evil dent from the following detailed description tak- I en in conjunction with the accompanying drawing in which:

Figure 1 isa top plan view of a rectifier bridge embodying my invention.

Fig..2 is a view on line lI-II of Fig. 1 with parts in section and.- in elevation.

Fig. 3 is an enlarged, view of the rectifler'portions of Fig. 2.

'Fig. 4 is a modification of the rectier construction of Fig. 2.

Fig. 5 is a still further modification of the rectifier construction of Fig. 2.

Fig. 6 is a diagrammatic view of the circuit of the bridge in Figs. 1, 2, land 5.

' Fig. 7 is a' top view of a rectifier element similar in shape to those of'Fig. 5 but of smaller diameter.

Figs. 8 and 9 are modicationsof theirectifying surfaces and contact arms of those shown in Fig. 2.

The standard construction of contact rectiflers such as represented by the most important class therein is a copper disc generally about threefourths to one and one-half inches in diameter' with one side oxidized. It has been found, however, that these copper discs have a very increased resistance for small currents. A threefourths inch diameter disc will have 20 ohms resistance at 20 milliamperes, 30 Aohms-at 10 milliamperes and then greatly increase to about 800 ohms as the current approaches zero. This varying and increasing resistance when the current -is below a milliampere has disadvantages due to the'big change in resistance with small fluctuations in the .current strength.

Another disadvantage with the standard constructure isy that due to the extensive area of `the rectifying disc a bridge would have a large electrostatic capacity and if the alternating cur-A rent increased in frequency above the commercial 60 cycles, there was a tendency of the alter.-

nating current to pass directly through the bridge and not to passthrough the load.

Accordingly my invention` contemplates in' creasing the current density and reducing the electrostatic .capacity by decreasing the rectify- I5'. The next arm ing area in a rectifier bridge. This reduction in area provides `for working at a better portion of the resistance to current curve. .The smaller area of the rectifying elements also permits the use of the bridge with higher frequencies even of the order of radio broadcast frequencies;

In Fig. 1 I have disclosed one preferred embodiment of my invention. The ring I0 is of any suitablevinsulating material and has preferably attached-to its upper annular surface II a plurality of inwardly extending arms I2, I3 and I4. In the case of a bridge construction, these arms may be limited to the three shown, although any number, especially a multiple of three, might be provided. In general` four arms are required, AC, AC; inthe special case of Fig. 1, the -I- is the clamping members, hence only three other arms are required. These arms extend towards the central axis and are preferably bent downward as shown in Figs. 2 and 3. The inner ends of 'these arms are in serial contact relation and are superimposed on one another as disclosed in Figs. 2 and 3. I prefer to have the rectifying junction only att-he inner ends-of these arms. As shown more clearly in Fig. 3, the end of the arm I4 has a small copper oxide rectifying layer on its upper end surface I3 below it preferably has both its upper end surface .I6 and lower end surface I1 oxidized. The lower surface of the arm I2 also has the oxidized surface I8 thereon. Various ways may obviously be used to keep these contact surfaces in compressed engagement, lbut I one that is both simple and effective is disclosed in Fig. 2 wherein a .contact bar 20 preferably of copper extends across the under side of the annular ring IIJ and has a central raised portion 2| upon which the oxide junction I8 rests and makes contactv therewith.- Another bar 22, also `'preferably of copper, extends across the top of the annular ring and has-a conductive screw 23 passing centrally therethrough and making contact under any desired pressurewith the uppermostarm I4. Bolts 24 extend through the ring I0 to connect the bars 20 and 22 and also`to bind them securely to the ring IIJ. These bolts pass through suitable Vspacers 29, Suitable-connections 25 may be made to the bars and also connections 26, 21 and 28 to the-arms I2, I3 and I4, respectively.

It will be noted that the structure described V in Figs. 1, 2 and 3 forms a very simplified full`` wave rectifying bridge with the four necessary connections. The actual rectifying surface is very small and the bridge accordingly has a greatly reduced capacity over the standard construction.

25 of the bars 20, 22 and the negative load to the arm I3. If the alternating current enters by the arm I4 during one-half cycle, it will pass upwardly through the rectifying junction I5 to the screw 23 and bar 22 and through the load back 'to the arm I3 where it passes through the rectifying junction. I1 to the 4arm I2 to the source of current. On the next reversal of current the current will enter by the arm I2 and pass through 'the rectifying junction I8 to the bar 2l! and through the load and then back to the arm I3 and then through the rectifying junction I6 to the arm I4 back to the source of current. This type of bridge is diagrammatically lillustrated in Fig. 6.

Fig. 4 illustrates a still further modification and is, in fact, a little more simplified than that of Fig. 2. A U-Shaped conductive member 30 has a screw 3i passing through the end of one of its arms and compressing three conductive arms 32, 33 and 34 between the tip of its screw and the other arm of the U-shapedmember 30. These arms 32, 33 and 34 have the copper oxide surfaces 35, 36, 31 and 38 arranged similar to that illustrated in Fig. 3.

Fig. 5 illustrates a still further modication in which the rectifying surfaces are made separate from the contact arms. In this figure, four tiny rectifying units 40, 4 I, 42 and 43 have one of their surfaces oxidized. These rectifying units may be little cylinders having a diameter such as that actually represented'in Fig. '1. The contact arms 44, 45, 46 are placed between these four rectifying units and any suitable connecting means, such as the U-shaped member 41, connects the upper and lower units. Although various arrangements of the outside'surfaceand contact arms may be made, I prefer to have the outside surface of the unit 40 contact with the arm 44 and to have both the outside surfaces of the units 4I and 42 contact with the arm 45 and the copper oxideI surface 43 `contact with the arm 46. In this specific arrangement the alternating current connections will be made to the arms 44 and 46, while the positive terminal of the-load is made to the U-shaped member 41 and the negative terminal of the load to the arm 45.

In Fig. 8 I have disclosed how a suitable contact arm 50vmay have a still further reduced extension 5I extending from it and then have a small area 52 on this extension 5I oxidized for the rectifying junction. The larger area of the arm 50 makes the assemblage of the device easy.

, It is possible, however, to have the arm the same arms 44', 45 and 45, for example, may be depressed ves width as extension 5I throughout and only to oxidize a tiny area at one end.

Another modification is disclosed in Fig. 9 wherein the broad contact arm 60 is tapered down to a small area 6I at the very end and,V4 the upper surface of this end oxidized.

Other modifications may be made of the shape of the rectifying arms and rectifying units. Ihe

at their ends to hold the rectifying units 40, 4I, 42 and 43 in depressions. Various suitable materials may be used. 'I'he arms 44, 45 and 45, for example, may be of some impressionable mate- 'rlal. such as lead, that can be squeezed under Apressure into a tight contact with' the rectifying units. While I have discribed the contact rectirangement. fier as of the copperand copper oxide type, other less successful types of contact rectifier materials can be used.

An examination of the drawing will clearly disclose that the end of the contact arms in Figs. 1 through 4 and 8 to 9 and also the rectifying units in Figs. 5 and '7 can be made very small. The cross section of the rectifying surface is preferably below that of a square of an inch on a side or a circle inch in diameter. The invention is especially adapted for an actual rectifying surface less than .016 square inch. This last dimension is approximately that of a square 1/8 inch on a side.

In spite of the tiny rectifying surface, it will be noted that the devices illustrated can be very easily assembled dueto their large contact arms and the ease with which electrical connections can be made to these contact arms.

Although'I have shown and describedcertain specific embodiments .of my invention, I am fully aware that many modifications thereof are possible. My invention therefore, is not to be restricted except insofar as is necessitated by the prior art.

I claim as my invention:

l. A contact rectifier arm of copper having a greatly reduced portion at one end and an oxidized surface limited to said greatly reduced portion.

2. A contact rectifier arm having a greatly reduced portion at one end and an oxidized surface only on said greatly reduced portion, said oxidized surface having an area of less than .016 square inch. I

3. A contact rectifier bridge comprising three arms in radial arrangement with an end of one between the adjacent ends of the other two and contact means joining the outside surfaces of said two, said one of said arms having two rectifying contact surfaces and said other two arms -having rectifying contact surfaces on the contact side remote from said arm with the two rectifying contact surfaces.

4. A contact rectifier bridge comprising a plurality of copper arms, each having a portion of one end portion superiicially oxidized, said oxidized ends being superposed in contact and said arms being disposed in radial arrangement.

5. A contact rectifier bridge comprising three copper arms in radial arrangement with an end of one between the adjacent ends of the other two and contact means joining the outside surfaces of said ltwo, said one of said .arms havingf* two oxidized contact surfaces and said other two arms having oxidized contact surfaces on the contact side remote from said arm with the two oxidized contact surfaces.

6. A contact rectifier bridge comprising a plurality of copper arms, each havingva portion of one end portion supercially oxidized, said oxidized ends being superposed in aligned contact and with said arms radiating therefrom, and means maintaining said ends in aligned contact.

7. A contact rectifier bridge comprising a plurality of metal contact arms, each having a porv4tion of one end portion having a surface layer adapted to produce a rectifying junction, said ends with surface layers being superposed in contact and said arms being disposed in radialar- 

